There are so many themes out there from which you'll be choosing, you may get this feature as part of a theme. You may also be able to locate a plugin that will do this for you in every post. However, just to show you how to do something in the code to make a link to an author's site, I'll show you how we got the link in this image to replace what was in this box prior.
Actually, you should probably forego this step at this point, but you can come back here later if you need to do it this way.